[Bug 210351] Wrong setting baudrate for FTDI chip FT230X

[bugzilla-daemon@bugzilla.kernel.org]

https://bugzilla.kernel.org/show_bug.cgi?id=210351

--- Comment #1 from Johan Hovold (johan@kernel.org) ---
On Wed, Nov 25, 2020 at 05:14:18AM +0000, bugzilla-daemon@bugzilla.kernel.org
wrote:
> https://bugzilla.kernel.org/show_bug.cgi?id=210351
> 
>             Bug ID: 210351
>            Summary: Wrong setting baudrate for FTDI chip FT230X
>            Product: Drivers
>            Version: 2.5
>     Kernel Version: all
>           Hardware: All
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: USB
>           Assignee: drivers_usb@kernel-bugs.kernel.org
>           Reporter: svv75@mail.ru
>         Regression: No
> 
> Hello!
> 
> I have three chips FT232BL, FT232R and FT230X. I am using them as a VCP on
> Linux (Ubuntu 18.04). According to Application Note AN_120 from FTDI, the
> baud
> rate generators of all these chips have 8 sub-integer prescalers. Divisor =
> 3000000 / baudrate = n + 0, 0.125, 0.25, 0.375, 0.5, 0.625, 0.75, 0.875.
> Where
> n is an integer between 2 and16384.
> So, I measured real baud rates, for n = 2 in combination with all possible
> sub-integer prescalers.
> And it turned out that all sub-integer prescalers worked for FT232BL, FT232R
> chips.
> 
> And for the FT230X, only a few prescalers work correctly. The following shows
> exactly how prescalers behave:
> 0          - correct
> 0.125  - correct
> 0.25     - correct
> 0.375   - WRONG! (works like 0.125)
> 0.5        - correct
> 0.625    - WRONG! (works like 0.5)
> 0.75      - WRONG! (works like 0.25)
> 0.875    - WRONG! (works like 0.125)
> 
> The same for the other n.
> 
> I think it is a driver problem, it initializes the sub-integer prescaler
> incorrectly. Since under Windows FT230X works fine with all sub-integer
> prescalers.

Thanks for the report.

It sounds like your device behaves like a FT8U232AM, which only supports
0.125, 0.25 or 0.5, then. Are you sure Windows is able to use the
others?

Is the device type being detected correctly? What does the log say when
you plug your device in? Please also post the output of "lsusb -v" for
the device.

Johan

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